Factors influencing participants' engagement with an interactive text-message intervention to improve sun protection behaviors: "SunText" randomized controlled trial

There is growing evidence suggesting that text-message-based interventions are effective to promote sun protection behaviors. However, it is still unclear how engagement and adherence with the intervention messages can be optimized through intervention design. This study evaluated the effect of different combinations of personalized and two-way interactive messages on participant engagement with a theory-based skin cancer prevention intervention. In the SunText study conducted in February-July 2019 in Queensland, Australia participants 18-40 years were randomized to four different text message schedules using a Latin square design. This study analyzed if the order and intensity in which the schedules were received were associated with participants' level of engagement, and if this differed by demographic factors. Out of the 389 participants enrolled in the study, 375 completed the intervention period and remained for analysis. The overall intervention engagement rate was 71% and decreased from the beginning to the end of the study (82.2%-61.4%). The group starting with personalized, but not interactive messaging showed the lowest engagement rate. The intervention involving interactive messages three times a week for 4 weeks achieved the highest engagement rate. The intervention with increasing frequency (personalized and interactive three times a week for 2 weeks; then daily for 2 weeks) had lower engagement than intervention with constant or decreasing frequency. Engagement with two-way interactive messages was high across all intervention groups. Results suggest enhanced engagement with constant or decreasing message frequency compared to increasing frequency.